Shallow Relations? Not for me...

Does a sun sign truly define a person? Are we not a product of our environment and upbringing as well apart from other parameters? I am thinking all these because recently my cousin who visited me was telling how his girl friend being born in the same sun sign as mine had shallow relationships...and he was surprised when I said that I strongly believe having only deep and meaningful relations. Is it just him or is it a tendency for the newgen to typecast someone into something because they belong to a particular sign...? While it could be true that being under the same sign may give you certain set of basic characteristics, it would and can not make you a replica of other person belonging to the same sign. Afterall, we are people hailing from diverse regions brought up in diverse climes and hence we are bound to have diverse tastes. It would be senseless to compare an Arian hailing from South India to an Arian hailing from say Russia or Mexico...What could be similar would be that they may both tend to be adventurous or say have a drive to start something unique etc. and that's about it. Making weird comparisons would actually harm the relationship as you approach the person with preconceived notions. Right?